This invention relates to attenuation of electromagnetic energy, and is particularly directed to a foam absorber which is effective for attenuating electromagnetic energy especially for radar attenuation, over a broad range of frequencies.
The use of an open-cell foam substrate having a filler forming a conductive loading gradient as a light-weight broadband microwave absorber is known. However, when such prior art absorbers are flexed in many instances the elasticity of the foam is reduced to a point where upon continuing flexure, the loading material fractures and the conductive gradient is adversely affected. This is due in large measure to the fact that the conductive gradient loading material has a different flexibility from that of the foam and does not bend with the foam substrate upon flexure thereof.
In addition, prior art foam absorbers often suffer from the problem of improper distribution of the conductive ink filler material in the gradiently loaded substrate.
Accordingly, one object of the invention is the provision of an improved foam absorber for attenuation of electromagnetic energy.
Another object is the provision of an open cell foam absorber gradiently loaded with a conductive material which has a flexibility which closely matches the flexibility of the foam substrate.
A still further object is to provide a foam absorber having a dielectric gradient which attenuates electromagnetic energy or radar over a broad range of frequencies.
Yet another object is the provision of a foam absorber for attenuation of electromagnetic energy, having improved distribution of the gradiently loaded dielectric material within the foam substrate.
Still another object is to provide procedure for producing the improved foam absorber of the invention.